Rotary cutting heads of mining machines or machines for the driving of underground roadways or tunnels, are conventionally provided with a plurality e.g. 50-150 blocks welded in place, each to receive a replaceable cutter pick provided with a carbide tip, each block having a receiving bore to receive a close fitting shank of the pick either directly, or more usually with an interposed sleeve.
Pick replacement is normally required after a certain degree of wear, loss of a tip, or pick breakage, and has usually required manual removal e.g. by the use of a chisel, drift, hammer etc with risk not only of sparks but also of flying metal particles, requiring variable degree of manual force. However, for various reasons, some picks may be impossible to remove manually and can only be removed after removing the entire sleeve or, in some cases, the block. This may mean removal of the rotary cutting head from its machine for transport to the surface of a coal mine, or to a safe area, where burning and welding operation can be carried out.
In the planing of road surfaces in preparation for re-surfacing operations, rotary cutting drums of road surface planing machines are conventionally provided with possibly 150 blocks, each to receive a replaceable cutter pick provided with a carbide tip, each pick box having a receiving aperture to receive a wear sleeve, with a shank of the pick engaged in the sleeve.
The need to accommodate a relatively large number of picks around the external periphery of the drum of a road planing machine, constrains the size of pick that can be used, and typical road planing picks have shanks of say 20 mm or ½ inch diameter. The result is the inevitable breakage of a large number of picks and the consequent need to remove the remains of a broken pick from the receiving bore of a block in which aperture the shank is located, usually with an interposed wear sleeve. Even if breakage has not occurred, regular pick replacement is required to counter the effects of wear and/or loss of a carbide tip.
In one known mechanical removal system an operative engages in a drift, against an end face of the shank of the pick, to push or prise the shank from the sleeve, or hammers a wedge against the end face.
Another current mechanical system for pick extraction, but which is in extensive use, employs a two pronged fork with wedge tines, which tines are hammered by an operative under a collar of the pick specifically provided for extraction purposes. These extraction procedures might need to be repeated 100 times or more depending on the nature of the cutting drum and the number of blocks welded, in predetermined array, around its external periphery.
In EP 1064453 is a proposal for hydraulic extraction of the shank of a pick holder located in a blind bore, whereby the shank of a pick holder is provided with a sealing ring to seal against the shank-receiving bore of the block, and hydraulic pressure is applied to the end face of the shank. In this system, the end of the pick is exposed and so can be knocked out by a hammer, and/or a drift can be engaged with a groove in the pick head.
However, in extensive use is a sleeved system as shown in GB 2285464, and here the means of achieving sleeve extraction (the pick can again be removed manually) is to step the sleeve, to provide sealing rings at either side of the step, and to introduce hydraulic fluid to the zone between the sealing rings. Whilst this system provides a solution for sleeve extraction, manual pick extraction can still be problematical and/or hazardous.
Both the above proposals for hydraulic extraction, whilst achieving the desired results, require modification from industry standard, of sleeve and/or block.
Furthermore, it will be appreciated that whilst the majority of picks can be successfully removed with a lever or wedge, inevitably with an unfavourable combination of manufacturing tolerances of a shank diameter etc plus the impacts received by the pick in service, it may prove impossible to extract a seized or broken pick manually from its sleeve.